1977 Merc 500 Thunderbolt minor water jacket leak, should I fix it?

[hotrod53]

After the season concluded I noticed that I had a sign of a trickle of water coming out of the #1 spark plug area. I know that this 4 cylinder has no head, but a water jacket. I was wondering if I should pull the power head and fix this or not.

I talked to a marine mechanic who suggested that I first torque the bolts to 35, if that didn't work he suggested putting some silicone around the hole where the gasket is. I read once that these bolts tend to get gaulded, I was also told that torqueing these bolts is part of regular maintenance.

I would love to pull the water jacket and replace the gasket, but many of the bolts are down inside of the cowl, I would probably have to pull the power head to accomplish this.

 

[racerone]

Re: 1977 Merc 500 Thunderbolt minor water jacket leak, should I fix it?

Fairly simple to remove that cover.--Clean all the surfaces and install with a new gasket.----I do not believe you have to pull the powerhead off for this job.--If leak gets worse you risk ingesting water into the engine, which is not good.

 

[racerone]

Re: 1977 Merc 500 Thunderbolt minor water jacket leak, should I fix it?

Please note change above,----No need to remove powerhead to change cover gasket.

 

[Chris1956]

Re: 1977 Merc 500 Thunderbolt minor water jacket leak, should I fix it?

No need to remove waterjacket, IMHO. Your mechanic is partially correct, silicone will fix the leak. If you use black silicone, it won't even show.

Those waterjacket bolts are only 1/4-20. I think 35 Ft-LB of torque will break them. Standard torque is 8 Ft-LBs. Likely some of them will break if you try to remove them as recommended, especially, if the motor has seen salt water. Best let sleeping dogs lie.....

 

[hotrod53]

Re: 1977 Merc 500 Thunderbolt minor water jacket leak, should I fix it?

Chris1956.... precisely why I ask. Although it's never been in salt, if I break bolts I'm screwed.

The boat is outside covered in about 3" of snow on top of the cover, I'll get a better look soon.

 

[racerone]

Re: 1977 Merc 500 Thunderbolt minor water jacket leak, should I fix it?

Some of the newer blocks are 1/4-20 threaded into the block.....The older motors used 1/4-28 with a nut external to the block.-Penetration fluid will help on those.---In fresh water I see no problems doing this job.

 

[jbjennings]

Re: 1977 Merc 500 Thunderbolt minor water jacket leak, should I fix it?

No need to remove waterjacket, IMHO. Your mechanic is partially correct, silicone will fix the leak. If you use black silicone, it won't even show.

Those waterjacket bolts are only 1/4-20. I think 35 Ft-LB of torque will break them. Standard torque is 8 Ft-LBs. Likely some of them will break if you try to remove them as recommended, especially, if the motor has seen salt water. Best let sleeping dogs lie.....

I'm just a hobbiest, but the above post is what I'd do. I have removed the jacket cover from 3 early 70's mercs (all freshwater) and I think 2 out of 3 had at least 1 broken bolt, as many as 3.
JMO,
JBJ

 

[Chris1956]

Re: 1977 Merc 500 Thunderbolt minor water jacket leak, should I fix it?

JBJ, try to repeat that success with a saltwater motor. I think all but about 3 broke on my IL6, eventhough I used heat and penetrating oil and an impact driver. I ended up drilling thru the casting and installing nuts on the backside.